Non-thermionic electron sources are known in the art and are commonly employed as electron sources wherein electrons are accelerated from an electron emitting surface into an adjacent free space region. In practice, electron emission is realized by providing very high electric fields on the order of 3.times.10.sup.7 Volts per centimeter (V/cm) at a surface of the electron emitter material. Such high electric fields typically are realized by providing electron emitter structures having a geometric discontinuity of a small radius of curvature as a method of enhancing the electric field strength.
Alternatively, electron sources or emitters are made of materials or surface coatings exhibiting a low surface work function (less than approximately 4 electron volts) in order to achieve appreciable electron emission with a reduction in the requirement of electric field enhancement.
Field emission electron sources of the prior art are typically controlled by modulating a voltage which is employed to provide the electron emission inducing electric field at the electron emitter.
Surface area electron emitters, such as diamond material electron emitters, have recently been introduced which provide appreciable electron emission at electric fields on the order of approximately 50.times.10.sup.3 V/cm.
An operational detriment of this new type of electron emitter is that desirable control of the electron emission inducing electric field is not practical for most applications.
Accordingly, there exists a need for an electron emitter which overcomes at least some of the shortcomings of the prior art.